But what about people? We often think of our professional network as a continuously expanding thing. Meet someone new, add them to the list. The list gets longer, your opportunities get ever wider. It may not be that simple, though. Just as we discard some skills in order to pick up others, it’s smart to focus on different types of people who can offer you the most support depending on the place in your career where you find yourself.

Here’s how to know who are the most valuable players in your professional network at each stage of your working life.

When you’re just starting out, it’s pretty obvious who the most useful people in your network are—mainly because you haven’t actually been in the workforce to build a professional network. So as new grads have found for generations, family connections and alumni groups are still your best bet.

According to Michele Mavi, director of internal recruiting and content development at Atrium Staffing, it can be tough to know whether personal contacts or academic ones will prove more helpful overall. A lot of that’s situational. "If there’s a job open at your mom’s best friend’s firm," she says, "then that may be the best contact, whereas if you get a hold of someone in your alumni network for an informational chat, they may say, ‘Great, keep in touch with me but we don’t have anything now.’"

Or it could be exactly the reverse, where your mom’s best friend has your dream job and is glad to talk with you, but the alumni job boards are where the actual openings are.

"The alumni network is really so powerful," Mavi says. "In this day and age when people are so super-connected," Mavi says, alumni are more likely to lend a hand to a new grad in need than they might’ve been previously. "It’s like your whole university becomes your fraternity."

"It’s like your whole university becomes your fraternity."

School contacts can be especially useful at the graduate level, Mavi points out. And while many MBA graduates, for instance, have often had considerable work experience before enrolling in business programs, many advanced degree-holders go straight to the top from undergrad. And when those people finally enter the workforce, they usually find the hyper-passionate colleagues they’ve made at the graduate level to be their strongest professional resources.

One thing Mavi says she’s noticed changing? Associate-level workers utilizing recruiters to help give them a boost after their first few years in the workforce. A recruiter herself, Mavi says she realizes "that’s going sound self-serving to a certain degree," but she’s in a position to spot such a change.

Recruiters, Mavi says, "used to be just for executive-level people and people in temporary jobs," but she believes the stigma associated with headhunters and their ilk is beginning to dissipate as younger workers begin reaching out for professional help. The reason, in her view, is that "when you’re at an associate level, you’re really looking for that next step. It’s really a numbers game—all those people are looking to move into that junior-manager role," and fewer factors may set them apart as there are among candidates for senior-level positions.

Choosing the other key player to help you advance your career after several years in the workforce, Mavi says, depends on where you want to go next. If you’re looking for a new employer, then "a manager that you’ve previously worked for who’s moved onto another company can be a great person to stay connected to."

Otherwise, if you’d prefer to stay put, "a senior person within your own organization who can serve as a mentor or advocate for you to start moving up" is your best bet. The key, in either case, is to use those first few years to build relationships with people one or two levels your senior.

It’s at mid-career that the contacts outside your own company may begin to matter more for you, says Mavi. The people to focus are "really going to be your peer group and your previous colleagues who’ve moved on, especially to competitors."

The competition is "always happy to talk," Mavi adds. "That’s usually where your experience at that level will be more relevant," and it’s arguably becoming more important than ever to have inside contacts who can speak to it directly.

Why? Because "in ’08, when the market tanked," Mavi explains, "companies were really reluctant to hire. Once they started hiring again, there were so many candidates available in the marketplace that had the exact skills they were looking for. And even though the job market corrected itself . . . that mentality hasn’t really left hiring managers."

They want to know what you’ve already done—which means they need someone who can vouch for the concrete results you’ve delivered in the past and how you did it.

Mavi isn’t the only recruiting professional who emphasizes the power of referrals in today’s job market, even as power is said to be tilting back into job seekers’ hands. In Mavi’s view, that’s because "transferrable skills" may be less appealing to prospective employers than they once were.

"Even though your skill set may be transferrable," she says, "people don’t really recruit that way anymore." They want to know what you’ve already done—which means they need someone who can vouch for the concrete results you’ve delivered in the past and how you did it. Which means contacts who were right there with you when that happened.

Once you’re at the upper reaches of the career ladder, it can be tempting to rub elbows mainly just with the other people there. But if it was your peers who helped you most around mid-career, they may not always be your most powerful contacts at senior levels.

"You can’t devalue people who are less experienced than you; maybe someday they’re going to be the ones in a hiring position."

It’s "the people you’ve previously managed" that Mavi suggests staying in touch with. "If they’re now at another organization [that’s] looking for another high-level role to fill, they can go to whoever it is in that C-suite and say, ‘Confidentially, my old boss at X-Y-and-Z would be a great fit.’" Of course, the prerequisite to benefitting in this type of situation is having been a good boss and mentor earlier on.

"You can’t devalue people who are less experienced than you," says Mavi. "They’re creating innovative companies. They’re people who can offer even more senior people something to learn from. And maybe someday they’re going to be the ones in a hiring position."

This openness to people at all levels of experience doesn’t just benefit late-career professionals, Mavi adds. Now that Facebook and LinkedIn are standard networking tools, she says, "the whole idea of networking overall is accepted." The notion that it was somehow inappropriate or a waste of time to reach out to someone you don’t know is now passe.

And that’s a good thing, she says. "Regardless if you’re senior level or junior level, people are very willing to talk to other people."